A well known problem with polymer electrolyte membranes (PEMs) used in fuel cells, such as direct methanol fuel cells (DMFCs), is the recovery of water from the cathode for both hydration of the PEM itself and for re-introduction into the anode fuel reactant stream where in the case of DMFCs, it serves both as a reactant and a dilutant for the methanol fuel. Water is also used as one of the reactant species in the fuel reaction for other types of PEM fuel cells which include those for which there is a reaction external to the fuel cell such as the reforming of hydrocarbon fuels, or those for which a chemical compound is reacted with water to produce hydrogen such as sodium borohydride. Water can also be used to humidify the reactant gas streams which enter the anode compartment of the fuel cell.
The conventional “active” solution to this problem involves putting a condenser and liquid separator on the cathode exhaust stream in order to collect liquid water, which is then metered back into the anode loop.